A tuning-fork vibrator, produced by cutting a piezo-electric material such as, for example, a crystal into a tuning fork configuration, may sometimes be incorporated in an oscillation circuit for obtaining a reference signal. Such a tuning-fork vibrator is usually mounted by supporting its base portion. When proper vibration frequencies of the two legs of the tuning fork are not equal to each other, that is, when they are not in equilibrium, a leakage oscillation develops in the base portion and if the base portion is supported with the vibration frequencies left unbalanced, the vibration frequency of the tuning fork deviates from its original vibration frequency and its Q is degraded. To avoid this, the tuning-fork vibrator has heretofore been supported softly to avert the influence of the support of the vibrator on its vibration frequency. Accordingly, when the tuning-fork vibrator is incorporated, for example, in a moving member, it has been difficult to obtain a support structure which supports the vibrator sufficiently even when subjected to a mechanical shock.
In view of the above, it has been proposed to correct imbalance of the vibration of the tuning-fork vibrator to thereby stabilize its vibration. With this method, since a leakage vibration develops in the base portion of the tuning-fork vibrator when its vibration is unbalanced, that is, when the proper vibrations of both legs are not in equilibrium, the leakage vibration is measured and, from an increase or decrease in the leakage vibration in the base portion, it is calculated predictively as to which one of the legs should be ground and how much, and then, based on the calculation results, grinding is conducted to bring the proper vibrations of both legs into agreement with each other.
The vibration frequency of the tuning-fork vibrator can be controlled by selecting the lengths of its legs; in general, the legs are formed in advance longer than a value which would yield a frequency desired to obtain and then the legs are ground shorter to approach the desired frequency. By the way, it is the general practice in the prior art to work the legs of the tuning-fork vibrator so that their proper vibration frequencies may be equal to each other or in equilibrium, that is, no leakage vibration may occur in the base portion and then to grind the both legs an equal length, thereby obtaining the desired frequency. In the case of such frequency regulation, if the proper vibration frequency of the vibrator prior to the working appreciably deviates from the desired frequency, even when the legs are correctly worked to reach the equilibrium state first and then they are each ground accurately by the same length, it may often happen, in practice, that the vibrator thus worked becomes unbalanced. The reason is that this method is based on the assumption that the vibrator is uniform all over and when the uniformity is lost, even if slightly, the equilibrium is destroyed in the process of making the vibration frequency of the vibrator approach the desired frequency after the equilibrium working.
In contrast to the foregoing, it has been considered to cut out a tuning-fork vibrator in a configuration which has an oscillation frequency as close to the desired frequency as possible and then subject it to equilibrium working to make the vibration frequency further approach the desired frequency. To perform this, it is necessary to cut out the vibrator so that its vibration frequency may be very close to the desired frequency but this requires a very high degree of accuracy; otherwise, the vibration frequency would become higher than the frequency desired to obtain, resulting in no frequency regulation becoming possible. Accordingly, in view of the actual manufacturing techniques that are presently available, it is not practical in terms of productivity and manufacturing costs to cut out first, with such high accuracy, a tuning-fork vibrator having a vibration frequency close to the desired frequency.
Further, it can also be considered to make the vibration frequency of the vibrator approach the desired frequency by performing the equilibrium working first and then checking whether the desired frequency is reached and, if not, effecting the equilibrium working again; but this method is defective in that the working time is long.
An object of the present invention is to provide a method for the frequency regulation of a tuning-fork vibrator by which the vibrator is cut out relatively simply so that its vibration frequency may be appreciably lower than a desired frequency and by which the tuning-fork vibrator can be adjusted correctly to the desired frequency and well-balanced.